The study included 20 patients and 10 normal control subjects with a clinical diagnosis of myasthenia gravis. The patients were classified according to Osserman and Genkins classification (grade 0, I, II a, II b, III and IV). Conventional EMG and nerve conduction studies were done to exclude neurogenic or myopathic changes. Repetitive nerve stimulation was carried out to the left ulnar, right spinal accessory and facial nerves. Voluntary single fiber electromyograpghy was carried out to the left extensor digitorum communis muscle and surface stimulation single fiber electromygraphy to the abductor digiti minimi. Acetyl choline receptor autoantibody titre was determined for each patient. The results of these tests were correlated to the clinical data. Single fiber electromyography showed the highest sensitivity.